TLC Spot Extraction & Compound Isolation for UV ID

[~christina~]

I am wondering what is the best method to use to extract a compound that is separated by TLC by the liquid extraction method following spot isolation (visualization using UV and scraping absorbent silica from plate) for identification by UV spectroscopy.


I originally used methanol for extraction of the unknown compound and analyzed solution with plain methanol for the reference solution. Problem is that I read that methanol dissolves silica gel. I assume that this would affect the spectra? (not sure how)

1. Assuming that it would affect the qualitative identification of a compound by UV , would the problem be solved by using a reference solution of methanol (after using it to 'extract' silica scraping from part of plate without desired compound).

Or should I just use ethanol, separate extract, dry and then redissolve residue in whatever solvent I need compound to be in?

2. Second issue is that I need the compound in different pH solutions (10 & 2). Could I use the acidic/basic aq solutions for extracting silica or would that dissolve it as well ? From what I read, extreme pH will dissolve the silica gel coating. Is the solution for this to also extract using a volatile solvent (having trouble picking one that will leave gel and extract out compound), drying, and redissolving it at needed pH?

Thanks

 

[DrDu]

Silica gel dissolves in methanol? Sounds strange to me. You could of course try it out and extract some clean silica gel with methanol and compare the spectrum with that of pure methanol.

 

[~christina~]

Silica gel dissolves in methanol? Sounds strange to me. You could of course try it out and extract some clean silica gel with methanol and compare the spectrum with that of pure methanol.

What I'm referring to is from what I read here: http://www.chemicalforums.com/index.php?topic=50163.0

I was going to try what you mentioned from a practical point but was wondering if anyone knew about this.

Also, what about my second dilemma regarding extraction to solutions of different pH and effect on the silica gel? Would I have to use organic solvent to extract, dry the solvent and then redissolve compound in aqueous base/acid solution?